Recent technological advances have allowed for a proliferation of digital media, which may include images of crimes being committed. For example, child pornography, statutory rape, masked gunmen, and other crimes may be captured on digital media such as digital images and video. This media can be used as evidence in legal cases, but commonly the perpetrator in the images can not be identified since his face is obscured and the images don't contain any traditional biometric data like fingerprints or palm prints.
Notably, among major categories of crime, child sex abuse has the lowest percentage of suspects prosecuted among all offenses. A declination for prosecution by U.S. attorneys does not mean that the suspect did not commit a Federal offense. The major reason for these declinations is weak/inadmissible evidence. Accurate biometric identification of suspects in child sex abuse cases and other crimes evidenced in digital media would greatly enhance the ability of prosecutors to achieve convictions.
Child pornography can include images of nude children or self-pornography that includes self photography of sexual acts with children. Criminals are usually careful to not show their faces in self-pornography for fear of identification. However, it is not uncommon to be able to observe bare skin of other body parts (such as the thighs) of the abuser. Thus, it may be desirable to identify a person based on areas of skin noted in digital photographs of these and other criminal acts.